Color cathode ray tube with radiation-emitting strip-like indexing areas having serrated edges



y 6, 1969 R. D. THOMPSON 3,443,139

COLOR vCATHODE RAY TUBE WITH RADIATION-EMITTING STRIP-LIKE INDEXING AREAS HAVING SERRATED EDGES Filed April 19, 1968 Sheet of 5 INOEXING SIGNAL u'nuznnou MEANS u INVEHTOL E4. 06m DTHom sou AGENT y 6, 1969 R. D. THOMPSON 3,443,139

' COLOR CATHODE RAY TUBE WITH RADIATION-EMITTING STRIP-LIKE INDEXING AREAS HAVING SERRA'IED EDGES Filed April 19, 1968 Sheet 3 of 3 NEMTOL K0659. D.TH9MPson BY 2 g men-r y 6, 1969 D. THOMPSON 3,443,139

R. COLOR CATHODE RAY TUBE WITH RADIATION-EMITTING STRIP-LIKE INDEXING AREAS HAVING SERRATED EDGES Filed April 19, 1968 Sheet 3 Of5 uuvEuTnL Y [Local 0. Tuomwsou flbENT United States Patent US. Cl. 313-92 10 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a color picture tube of the feedback or sensing type wherein the electron sensitive screen comprises a series of groups of different color emitting phosphor strips and a series of serrated-edge indexing strips or exposed strip-like areas extending parallel to the color phosphor strips and perpendicular to the direction of beam scan. Beam-produced radiation from the indexing strips is utilized to synchronize the application of color signals to the beam with the instantaneous position of the beam on the screen. The serrated edges of the indexing strips may be simple rectangular-teeth of suitable length, stepped teeth, or sinusoidal teeth.

Background of the irzvemion This invention relates to image reproducing devices for producing color images and particularly to cathode ray tubes having a luminescent screen which includes means for generating indexing signals for the purpose of synchronizing the scan and color modulation of an electron beam with each other. Such tubes are sometimes known as feedback or sensing tubes. One such tube disclosed by the prior art includes a mosaic luminescent screen comprising an array of color phosphor groups, each of which includes a plurality of different coloremitting phosphor strips parallel to each other and perpendicular to the direction of beam scan. A plurality of spaced-apart short-persistence phosphor strips is disposed adjacent to the back of and parallel to the color phosphor strips. For example, the short persistence phosphor may be ultraviolet emitting. The tube envelope is provided with a -UV transmitting window positioned behind the luminescent screen, whereby a UV-sensitive phototube outside the cathode ray tube can pick up UV indexing signals which are generated when the electron beam scans across the spaced-apart UV phosphor strips. The indexing signal derived from the indexing strips provides information regarding the actual instantaneous positon of the electron beam on the screen with relation to the color of light being produced. The indexing signal is employed in a servo system to insure the application of the proper electrical color signal to the electron beam at all times.

Alternatively, the material of the indexing strips could be secondary emissive, and means could be provided within the tube for collecting the radiation from the strips.

In my Patent No. 2,962,546 I disclosed that video pulling, that is, distortion of the indexing signal by the color modulation applied to the beam, could be minimized by making the frequency of the indexing strips (and the signal produced thereby) different from the color group frequency of the phosphor strips, and by constructing the indexing strips with a sine wave distribution in thickness or phosphor efficiency so that the indexing signal is a sine wave free of harmonics. However, it is diflicult to make variable thickness indexing strips with the ideal sine wave distribution. A plural-step approximation thereof is shown in FIG. 4 of the patent. With the proportions shown in FIG. 4, the video pulling of that approximation would be about 10 degrees.

3,443,139 Patented May 6, 1969 Summary of the invention An object of the present invention is to provide an improved screen structure for a sensing type cathode ray tube.

In accordance with the invention, the luminescent screen of the sensing type cathode ray tube is provided with UV emitting indexing strips or exposed strip-like indexing areas of variable width. For example, serrated-edge strips may be deposited on the mosaic of color phosphor strips, or on a thin light reflective coating on the mosaic. Alternately, a continuous layer of UV indexing phosphor material may be deposited on the color phosphor mosaic (or the aluminum coating), and spaced-apart serrated strips of inactive material, such as graphite, may be deposited on the UV layer to mask off all but the desired serrated strip-like areas thereof. The inactive material must be opaque to UV radiation. While the serrations on the edges of the indexing strips or areas may have a simple rectangular shape for easy manufacture, lowest video pulling is produced by a sinusoidal serrated edge having a width of about 0.133 times the width of the indexing cycle.

Brief description of the drawing FIG. 1 is a perspective view, with parts broken away and the interior greatly enlarged, of a sensing-type color cathode ray tube embodying the invention;

FIG. 2 is an enlarged view of a portion of the luminescent screen shown in FIG. 1;

FIG. 3 is a section view taken on the lines 3-3 of FIG. 2;

FIG. 4 is a graph showing approximately the indexing signal produced by an elliptical beam spot shape in FIG. 2;

FIG. 5 is a view similar to FIG. 2 of a modification thereof;

FIG. 6 is a graph showing approximately the indexing signal produced by an elliptical beam spot in FIG. 5;

FIG. 7 is a view similar to FIG. 2 of another modification thereof;

FIG. 8 is a graph showing approximately the indexing signal produced by an elliptical beam spot in FIG. 7;

FIG. 9 is a view similar to FIG. 2 of a further modification thereof;

FIG. 10 is a view similar to FIG. 2 of still another modification; and

:FIG. 11 is a section view taken on the line 11-11 of FIG. 10.

Description of the preferred embodiments In FIG. 1 is shown a cathode ray tube 10 comprising an envelope 12 having a luminescent screen 14 disposed on an internal end surface thereof. An electron gun 16 disposed in the envelope is adapted to project an electron beam onto the screen 14. A window 18 is provided in the envelope 12 rearwardly of the screen 14 for a purpose hereinafter described.

The luminescent screen 14 includes a mosaic 20 of different color emitting phosphor strips. The color strips may for example comprise successive strips of red-emitting, green-emitting and blue-emitting phosphor, designated in the drawing as R, G and B, respectively. The mosaic 20 is made up of a plurality of recurring groups 21, each of which includes one each of the R, G and B strips. The specific character of the color phosphor groups 21, for example, the width of the color strips, the color emission thereof, the number of strips for each group, and the color arrangement within each group, may be chosen in accordance with known practice.

Preferably, a light reflective layer 22 is superimposed on the back of the mosaic 20, i.e. on the side facing towards the electron gun 16. If included, the layer 22 may, for example, comprise a thin electron-transparent layer of aluminum which is disposed on the color mosaic 20 in accordance with known practice.

Superimposed on the light reflective layer 22 IS an array of spaced-apart strips 24 of indexing material. The indexing strips 24 are preferably made of a phosphor which emits very short-persistence ultraviolet luminescence when excited by an electron beam. For example, a cesium-lithium activated calcium-magnesium-silicate phosphor known as P-l6 may be used.

In accordance with the present invention, each of the indexing strips is formed with serrations in each side or edge thereof, for reducing video pulling. In the embodiment shown in FIGS. 1-3, the serrations are formed by longitudinally-spaced rectangular teeth 26 extending outwardly from a continuous middle portion 28 of the indexing strip 24.

Preferably, the width of the teeth 26 and the rectangular spaces 30 therebetween should be small compared to the height of the beam.spot, that is the beam dimension parallel to the color strips 21, and the spaces 30 between the teeth should have a width substantially equal to the width of the teeth 26, as shown in FIG. 2. The cycle width D of the indexing strips 24, as measured between corresponding points on adjacent strips, is preferably equal to the width of three groups 21 of the color phosphor strips, as also shown in FIG. 2. The average width of each strip 24 is equal to one-half the cycle width D.

The beam is preferably shaped, by suitable beam forming and focusing means, to produce a vertically-elongated spot having rounded corners, e.g. an elliptical spot, as shown by the dotted ellipse 32 in FIG. 2. The curve 33 in FIG. 4 shows approximately the shape of the indexing signal wave produced by scanning the indexing strips 24 of FIG. 2 by an unmodulated elliptical beam spot 32.

It can be shown theoretically, and it has been demonstrated experimentally, that the lowest video pulling is produced with the type of serrations shown in FIG. 2 when the width of the serrated edge of each strip 24 is approximately n/12 of the cycle width D of the strips, where n is 1, 3 or 5. In FIG. 2, where n=1, the amount of video pulling is no more than about 2 degrees when the tube is operated to produce a saturated color.

In the modification shown in FIG. 5, the indexing strips 34 have teeth 36 that are three times as long as the teeth 26 in FIG. 2. Thus, n=3, and the width of the serrated edge is of the cycle width D. The approximate shape of the three-level indexing signal produced by an elliptical beam spot 32 in FIG. is shown by the curve 38 in FIG. 6.

FIG. 7 shows a modification of FIG. 2 wherein the simple rectangular teeth 26 are replaced by stepped teeth 46 on indexing strips 44. The width of each step should be about of the cycle width D. FIG. 8 shows a curve 48 of the approximate indexing signal produced by an elliptical beam spot 32 in FIG. 7. It can be seen that the signal 48 in FIG. 8 is very similar to the signal 33 in FIG. 4.

FIG. 9 shows a modification of the screen of FIG. 2 wherein the indexing strips 24 are replaced by spaced indexing strips 56 the edges of which are formed with sinusoidal-shaped serrations 58. The optimum width of the sinusoidal serrated edge for minimum pulling is about .133D, in which case the video pulling is less than 1.

FIGS. and 11 show a modification of FIG. 2 in which a continuous layer 60 of indexing material is deposited on the reflective layer 22 and the desired serrated edge strip-like areas of exposed indexing material are formed by masking 01f portions of the indexing layer 60 by means of serrated edge masking strips 62 of inactive material, as described in my Patent No. 3,280,358 for masking strips of uniform width. In the particular case shown, wherein the average width of the indexing strips is equal to one half the cycle width D, the shape of the serrated masking strips 62 may be identical with the shape of the serrated indexing strips 64 in FIG. 2. That is, the masking strips 62 may be formed with rectangular teeth 64 and intermediate spaces 66 which are identical in shape to the teeth 26 and spaces 30 in FIG. 2. The masking strips 62 may be made of graphite, for example.

FIG. 11 also shows a modified color phosphor strip arrangement wherein the individual color phosphor strips of different colors, e.g. R, G and B, are separated or spaced apart by inactive guard band strips 68, to permit the production of saturated colors with a larger beam spot.

The mosaic 20 of different color emitting phosphor strips in FIG. 3 can be produced by known methods, such as by a sequence in which each set of strips of the same color is obtained by application to the envelope 12 of a photosensitive suspension of phosphor particles capable of luminescing in a particular color, exposure to active light through a photographic pattern composed of elongated clear and opaque areas, and development to remove phosphor particles in areas not exposed. The light reflecting layer 22 can be applied in known manner by evaporation. The serrated indexing phosphor strips 24 can be applied by a photographic printing method like the color phosphor strips. The continuous indexing phosphor layer 60 of FIG. 11 can be applied to the layer 22 by spreading through rotational forces a suspension of phosphor particles in a viscous vehicle, a portion of which evaporates and another portion of which remains as a binder to permit subsequent applicationpf a serrated edge indexing pattern of opaque material forming the masking strips 62. A suitable process is one in which a layer of polyvinyl alcohol (PVA) sensitized by potassium dichromate is applied to the layer 60 and exposed to light through an appropriate photographic pattern of opaque and transparent areas, and unexposed areas are removed by solution in water. Graphite particles are then applied in a uniform layer by settling or spinning. A water spray then removes graphite particles from the bare areas but not from the tacky surface of the PVA pattern. This method can also be used to produce the guard band strips 68 in FIG. 11.

I claim:

1. An image reproducing device comprising an image screen and electron gun means to project an electron beam towards said screen, said screen including a plurality of light emitting strips arranged to be energized by said beam, and indexing means disposed to be energized by said beam to thereby produce an indexing signal, said indexing means comprising a plurality of strip-like areas of indexing material extending parallel to said light emitting strips and disposed to be energized by said beam, each of said strip-like areas having serrated edges.

2. A device as in claim 1, wherein said screen includes an electron transparent light reflective layer interposed between said indexing means and said light emitting strips.

3. A device as in claim 1, wherein each of said serrated edges is made up of substantially rectangular indexing areas separated by substantially rectangular inactive areas of substantially the same dimensions.

4. A device as in claim 3, wherein the dimension of said rectangular areas normal to said edges is approximately 12/12 of the distance between corresponding points on adjacent strip-like areas, where n is 1, 3 or 5.

5. A device as in claim 1, wherein each of said serrated edges is made up of stepped areas each having a dimension normal to said edges approximately equal to n/l2 of the distance between corresponding points on adjacent strip-like areas, where n is 1, 3 or 5.

6. A device as in claim 1, wherein said indexing means comprises a continuous layer of indexing material on said screen and spaced serrated-edge strips of opaque material disposed on said indexing layer and masking said layer except for said serrated-edge strip-like areas of indexing material.

7. A device as in claim 1, wherein said strip-like areas consist of spaced serrated-edge strips of indexing material.

8. A device as in claim I, wherein said serrated edges have a substantially sinusoidal shape.

9. A device as in claim 8, wherein the width of each serrated edge is approximately .133 times the distance between corresponding points on adjacent strip-like areas.

10. A color image reproducing device comprising an image screen and electron gun means to project an electron beam towards said screen, said screen including strips of a plurality of different colored light emitting materials arranged in repeating color groups to be energized at a given color group frequency by said beam, and indexing means disposed to be energized by said beam and to thereby produce an indexing signal, said indexing means being constructed so that said indexing signal has an in dexing frequency different from said color group frequency and harmonics thereof, said indexing means comprising a plurality of strip-like areas of indexing material disposed to be energized by said beam and extending parallel to said light emitting strips, each of said strip-like areas having serrated edges.

References Cited JAMES W. LAWRENCE, Primary Examiner. V. LAFRANCHI, Assistant Examiner. 

